#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#if 0
int main()
{
	
		char c = 0;
		int v0 = 0;
			int	v1 = 0;
			int	v2 = 0;
			do
			{
				switch (c = getchar())
				{
				case'a':case'A':
				case'e':case'E':
				case'i':case'I':
				case'o':case'O':
				case'u':case'U':v1 += 1;
				default:v0 += 1;v2 += 1;
				}
			} while (c != '\n');
			printf("v0=%d,v1=%d,v2=%d\n", v0, v1, v2);
			return 0;
	
	return 0;
}
#endif

int main()
{
	int i = 0;
	int j = 0;
	int count = 0;
	char n = 10;
	for (i = 0; i <= n - 1; i++)
		for (j = n; j > i; j--)
			count++;

	printf("%d", count);
	return 0;
}